1. Field of the Invention
The present invention relates generally to orthotic inserts for use in conjunction with various types of footwear. More particularly, the present invention relates to an orthotic insert constructed of layers of fiberglass and graphite fiber materials, with the graphite layers being configured to provide enhanced control over the motions of the foot, and the device further being particularly configured to provide a long service life without cracking.
2. Background
a. Orthotic Devices
Orthotic inserts are used in conjunction with various types of footwear to enhance the functions of a person's foot. An orthotic insert can be either soft or hard: a hard insert is a substantially rigid member, desirably having a relatively thin vertical thickness dimension and extending from the calcaneal area of the foot (the heel portion) to at least the metatarsal head area of the foot (i.e., the "ball" of the foot). In general, the purpose of the rigid orthotic (sometimes called a "functional orthotic") is to first position, and then control the movements of, the midtarsal and subtalar joints during the gait cycle which the body goes through in walking and running, and possibly other weight bearing activities.
b. The Gait Cycle
Before proceeding with a discussion of prior orthotic devices and the problems which have been encountered with the same, the "gait cycle" will be discussed here so as to provide an improved understanding of the function of the present invention. The discussion will include the following: (i) the main components of the human leg and foot, and how these function relative to one another; (ii) the gait cycle which a person goes through in a normal walking motion; and (iii) the intended function of a rigid orthotic in optimizing the coordinated operation of the person's foot and leg throughout the gait cycle.
(i) The Main Components of the Human Leg and Foot and How These Function Relative to One Another
FIGS. 1-3 show a typical human foot 10 and (in FIGS. 2-3) the lower part 12 of the leg 14. The two lower bones of the leg are the tibia 16 and the fibula 18. Below the tibia and fibula, there is the talus 20 (i.e. the "ankle bone"). Positioned below and rearwardly of the talus 20 is the calcaneus 22 (i.e. the "heel bone"). Positioned moderately below and forward of the talus 20 is the navicular 24 and forward of the calcaneus is the cuboid 26. Extending forwardly from the navicular are the three cuneiform bones 28. Extending forwardly from the cuneiform bones and the cuboid are the five metatarsals 30. Forwardly of the metatarsals are the phalanges 32 which make up the five toes 34.
The movement of the talus 20 relative to the tibia 16 and fibula 18 is such that it enables the entire foot to be articulated upwardly and downwardly (in the motion of raising or lowering the forward part of the foot). However, the talus is connected to the tibia and fibula in such a way that when the entire leg is rotated about its vertical axis (i.e. the axis extending the length of the leg), the talus 20 rotates together with the leg 14.
With regard to the relationship of the talus to the calcaneus, these two move relative to one another about what is called the "subtalar joint" indicated at 36. The subtalar joint can be described generally as a hinge joint about which the talus and calcaneus articulate relative to one another. On average, the hinge axis extends upwardly and forwardly at a slant angle of about 42.degree. from the horizontal, and also slants forwardly and inwardly at about 16.degree. from a straightforward direction. There is also a midtarsal joint 38, and this will be discussed later.
To explain further the hinge motion of the subtalar joint, reference is now made to FIGS. 4a and 4b. The talus can be considered as a vertical board 40, and the calcaneus as a horizontally extending board 42, these being hinge connected to one another along a diagonal hinge line 44, with this hinge line corresponding to the subtalar joint 36. It can be seen with reference to FIG. 4a that as the talus is rotated inwardly about its vertical axis (i.e. the front part of the leg is rotated toward the center of the person's body), there is a corresponding rotation of the calcaneus (i.e. the horizontal board 42) about a horizontal axis. It can be seen in FIG. 4b that an opposite (i.e. outward) rotation of the talus (i.e. the vertical board 40) causes a corresponding rotation of the calcaneus (i.e. the horizontal board 42) in the opposite direction to that shown in FIG. 4a.
With regard to the midtarsal joint 38, this is in reality composed of two separate joints, the talo-navicular and the calcaneal-cuboid. It is a complex joint, and no attempt will be made to illustrate or recreate its motion accurately. Instead, a somewhat simplified explanation will be presented as it relates to the present invention.
The main concern relative to the midtarsal joint is not the precise relative motion of the parts of the foot which make up this joint, but rather the locking and unlocking of the joint which occurs when there is an outward motion of the leg and talus and an opposite inward motion, respectively. When the leg is rotated inwardly, the midtarsal joint 38 is in its unlocked position so that the portion of the foot 10 forwardly of the joint (i.e. the midfoot 45) is flexible, this being the "pronated" position of the foot. On the other hand, when the leg and talus are rotated outwardly, the foot is said to be "supinated" and the midtarsal joint is in its locked position and the midfoot is essentially a part of a rigid lever. In actuality, the midfoot never becomes completely rigid, so that even in the totally supinated position, there is some degree of flexibility in the midfoot.
This function of the midtarsal joint will now be explained relative to FIGS. 5a and 5b. It can be seen that FIGS. 5a-b are generally the same as FIGS. 4a-b, except that a forward board member 46 is shown to represent the midfoot 45, this member 46 having a downward taper in a forward direction, and also a lower horizontal plate portion 48. This plate portion 48 is intended to represent that the plantar surface (i.e. the lower support surface) of the midfoot 45 engages the underlying support surface in a manner so as to remain generally horizontal to the support surface.
It can be seen that when the two board members 40 and 42 are in the pronated position of FIG. 5a, the midtarsal joint represented at 50 in FIGS. 5a-b is in a first position which will be presumed to be in unlocked position. In the unlocked position of FIG. 5a, the member 46 is not rigid with the horizontal member 42, and the forward member 46 can flex upwardly relative to the horizontal member 42. (This is the pronated position of the foot 10.) However, in the position of FIG. 5b, the board members 46 and 42 will be presumed to be locked to one another so that the members 42 and 46 form a unitary lever. For ease of illustration, no attempt has been made to illustrate physically the unlocking relationship of FIG. 5a and the locking relationship of FIG. 5b. Rather, the illustrations of FIGS. 5a-b are to show the relative movements and positions of these components, and the locking and unlocking mechanism is presumed to exist.
(ii) The Gait Cycle which the Person Goes Through in a Normal Walking Motion
Reference is first made to FIGS. 6a and 6b. As illustrated in the graph of FIG. 6a, during the normal walking motion, the hip (i.e. the pelvis) moves on a transverse plane, and this movement in the gait cycle is illustrated in FIG. 6b. Also, the femur (i.e. the leg bone between the knee joint and the hip) and the tibia rotate about an axis parallel to the length of the person's leg. It is this rotation of the leg about its vertical axis which is intrinsically related to the pronating and supinating of the foot during the gait cycles and this will be explained in more detail below.
There is also the flexion and extension of the knee, as illustrated in the five figures immediately below the graph of FIG. 6a. Further, there is the flexion and extension of the ankle joint. At the beginning of the gait cycle, the heel of the forwardly positioned leg strikes the ground, after which the forward part of the foot rotates downwardly into ground engagement. After the leg continues through its walking motion so as to extend rearwardly, the person pushes off from the ball of the foot as the other leg comes into ground engagement.
The motions described above are in large part apparent from relatively casual observation. However, the motion which is generally overlooked by those not familiar with the gait cycle is the inward and outward rotation of the leg about its lengthwise axis which must occur with the pronating and supinating of the foot. This will be described relative to FIG. 7a and FIG. 7b.
At initial ground contact the leg is rotated moderately to the outside (i.e. the knee of the leg is at a more outward position away form the center line of the body) so that the foot is more toward the supinated position (i.e. closer to the position shown in FIG. 4b). Consequently; the initial heel strike and loading of the foot takes place on the lateral (i.e. outer) side of the heel, and the calcaneus is normally inverted by approximately 2.degree. at heel contact. Immediately following heel strike and up to the 25% position, the leg rotates about its vertical axis in an inward direction so that the subtalar joint pronates. This pronation motion of the subtalar joint results in 4-6.degree. of eversion of the calcaneus, and ultimately this bone rests an average of 2-4.degree. degrees everted to the vertical when the 25% stance position is reached. The effect of this is to rotate the heel of the foot so that the center of pressure moves from a lateral heel location toward a location nearer the center line of the foot, as indicated at 54 in FIG. 7b. Also, the pronating of the subtalar joint produces a degree of relaxation of the midtarsal joint 38 and subsequent relaxation of the other stabilization mechanisms within the arch of the foot. Furthermore, this inward rotation of the leg serves as a torque converter; the internal rotation takes the vertical force of the leg at heel contact and converts this into a frontal plane force which extends the relaxed foot. From the foregoing, it will be understood that shock absorption at heel contact is thus primarily a function of controlled pronation of the foot during the first 25% of the stance phase.
With further movement from the 25% to the 75% position, the leg rotates in an opposite direction (i.e. to the outside), and the subtalar joint becomes supinated at the 75% position of FIG. 7a. This functionally locks the midtarsal joint so that the person is then able to operate his foot as a rigid lever so as to raise up onto the ball of the foot and push off with this as the other leg moves into ground contact.
With reference again to FIGS. 7b, the initial pressure point at ground contact is at 52, and moves medially across the heel to the location at 54. Thereafter, the pressure center moves rather quickly along broken line indicated at 56 toward the ball of the foot. As the person pushes off of the ball of the foot and to some extent from the toes, the pressure moves to the location at 58. Accordingly, it will be appreciated that the pressure point or center shifts from the lateral portion of the foot to the medial portion in the course of the normal gait cycle.
(iii) The Intended Function of the Orthotic to Improve Operation of the Person's Foot and Leg Throughout the Gait Cycle
A primary function of most orthotic inserts is to initially position the plantar surface of the calcaneus 22 and the midfoot 45 so that the subtalar and midtarsal joints 36 and 38 are positioned in the proper functional relationship for the person's foot, and to thus control the motion of the foot parts and the leg and hip throughout the gait cycle. It will be understood that if the components of the foot have the proper initial position and movement about the subtalar and midtarsal joints, the entire gait cycle, all the way from the coordinated rotation of the hips through the flexion and rotation of the leg, and also from the initial heal strike to the final toe-off, will be properly coordinated and balanced for optimum movement.
The only practical way that a foot can be controlled in this manner is by a three dimensional member which properly conforms to the foot's plantar surface. The insoles of mass-produced shoes, however, do not ordinarily conform to the plantar surface of any particular foot so as to optimally locate its components. Accordingly, it has been the practice for many years to provide an orthotic insert which engages both the shoe and the foot in a manner so as to properly orientate the internal components of the latter.
c. Deficiencies of Prior Orthotic Inserts
Orthotic inserts have been formed of many different materials, including acrylic plastic, leather, metal, and foam rubber, for example. One construction which has proven extremely successful in recent years is a composite material insert formed of fiberglass and graphite fiber in resin.
An exemplary orthotic insert having the latter construction is disclosed in U.S. Pat. No. 4,439,934, the inventor of which is the same as of the present invention. The insert is fabricated by placing layers of fiberglass, resin, and graphite fiber upon a positive cast. The first layer is a continuous sheet constructed from a cloth such as fiberglass or nylon mesh and impregnated with resin. The second layer is a continuous sheet of graphite with the woven graphite fibers preferably running diagonally. The next layer is also a glass and resin continuous sheet, and then another graphite continuous sheet is added with the woven graphite fibers running orthogonally. Finally, there is a bottom layer which may be a glass and resin continuous sheet similar to the top layer. The assembly is heat cured to provide a bonded structure, and is trimmed to the desired size and shape by cutting and grinding.
Orthotic inserts having this construction are very strong, yet extremely lightweight and relatively thin. In practice, however, it has been found that they exhibit a number of deficiencies. Firstly, devices of this type have been prone to develop serious cracking with extended use. The cracks usually develop along the medial and lateral (i.e., side) edges of the insert and, once established, quickly propagate and destroy the device. It has also been observed that the cracks sometimes occur in the toe or heal areas and extend longitudinally into the structure.
As part of the present invention, Applicant has discovered the unexpected source of this problem. It has been found that the serious cracks initiate at the sites of tiny, often microscopic "microcracks" which are formed along the edges of the device during the cutting and grinding phases of the manufacturing process; a great multiplicity of these microcracks are formed all along the edges of the device during final shaping and finishing. It has been found that those along the side edges are the most likely to enlarge, apparently due to the sagittal plane (i.e., end-to-end) bending to which the device is subjected as the person walks. However, the cracks may also propagate longitudinally in the heel and toe areas as a result of frontal plane flexing or "cupping" of the device.
As part of the present invention, Applicant has discovered that the severity of the cracking problem which is experienced by such composite material inserts stems primarily from the fact that, once the cracks start in the graphite fiber material, they propagate with extreme speed. Thus, even though the flexible fiberglass layers have been found to be far more resistant to cracking, their integrity is also destroyed once the associated graphite layer begins to break.
Another deficiency of such prior devices is that they have offered relatively little flexibility in terms of allowing the rigidity or other characteristics of the insert to be adjusted to satisfy the requirements of a specific foot. At the time of their introduction, composite material inserts having the construction described above represented a significant advance in this respect. However, the adjustments could only be made in the most general sense: By varying the orientation of the graphite sheets so that the fibers extended in various directions, the overall rigidity of the structure (or possibly in certain generalized areas) could be adjusted; also the rigidity of certain areas could be increased by thickening the structure, although this had the disadvantage of increasing the thickness of the plate itself. In short, the construction of the prior devices has offered little opportunity for "fine-tuning" of rigidity/flexibility and other control characteristics in specific areas where this may be needed to satisfy the requirements of a particular foot.
Accordingly, there has existed a need for a composite material orthotic constructed of layers of fiberglass and graphite fiber material which minimizes or eliminates the problem of cracks developing over a period of extended use. Moreover, there is a need for such a construction which permits the rigidity and other control aspects of the insert to be readily tailored to satisfy the specific needs of a person's foot, and particularly for allowing this to be done without necessitating a substantial increase in the thickness of the device. Still further, there is a need for such an improved orthotic which lends itself to being made by a relatively quick, convenient, and economical method.